How does one line up a 3D skybox model with a full-sized counterpart?

[Vel0city]

I've always wondered how Valve got the Hydro dam in the skybox to line up, even though it's a really tiny version in the skybox with full-sized models in the "real world" that blend together with the dam seamlessly.

Is there a magic trick to do this first try or is there a method for this (I assume it's the latter but you never know)?

 

[worMatty]

There is a trick. Read the guide about construction of 3D skyboxes here.

In summary, you copy the world brushes of your map in to the skybox and shrink them down to be sixteen times smaller. Give them a custom visgroup so you can toggle them on and off. You then use your new miniature brushes to align your skybox models and brushwork. Hide their visgroup when you want to compile. Pay particular attention to the steps involving the sky camera entity. It's used as a common central reference point between the map world and the skybox world.

 

[YM]

You could use visgroups, or you could make the mini geometry tools/skip and leave them on all the time. It's simpler.

If you want texture scaled as well, to line something up exactly then use texture scaling lock before performing the scale. This is SUPER useful!

 

[Skullio]

Are you asking how did they know how big to make the dam model? They probably had all the dimensions figured out beforehand but you can do it easily by blocking your model out in the map skybox with simple brushes and use the size as reference in the modelling program.

As long as you have the model program set up with the same grid as hammer it's pretty simple

 

[Another Bad Pun]

Create the 3D skybox scenery around the map with real proportions and then shrink it down 16X along with the sky_camera. (<TL> is needed, as YM pointed out) If you're careful and do it correctly, the transition between the real world and the 3D skybox should align perfectly, although there may be slight lighting differences.
Props are a little more difficult to deal with, but the general concept is the same and you can use skip brushes to align everything (also as YM said.)
This is how I do it atleast

 

[RodionJenga]

I would do as they say and make the skybox at real scale first, with the real scale models. When you shrink everything, the entity won't shrink, but changing it to the skybox version of the model should put it in the right place.
Alternately, make a brush the size of the real model and line them up, then use it to line up the skybox model once it's shrunk